This section provides background information related to the present disclosure which is not necessarily prior art.
High-energy density, electrochemical cells, such as lithium ion batteries can be used in a variety of consumer products and vehicles, such as Hybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs). Typical lithium ion batteries comprise a first electrode (e.g., a cathode), a second electrode of opposite polarity (e.g., an anode), an electrolyte material, and a separator. Conventional lithium ion batteries operate by reversibly passing lithium ions between the negative electrode and the positive electrode. A separator and an electrolyte are disposed between the negative and positive electrodes. The electrolyte is suitable for conducting lithium ions and may be in solid or liquid form. Lithium ions move from a cathode (positive electrode) to an anode (negative electrode) during charging of the battery, and in the opposite direction when discharging the battery. For convenience, a negative electrode will be used synonymously with an anode, although as recognized by those of skill in the art, during certain phases of lithium ion cycling the anode function may be associated with the positive electrode rather than negative electrode (e.g., the negative electrode may be an anode on discharge and a cathode on charge).
In various aspects, an electrode includes an electroactive material. Negative electrodes typically comprise such an electroactive material that is capable of functioning as a lithium host material serving as a negative terminal of a lithium ion battery. Negative electrodes typically include the electroactive lithium host material and another electrically conductive material, such as carbon black particles, as well as one or more polymeric binder materials to hold the lithium host material and electrically conductive particles together.
Typical electroactive materials for forming a negative electrode (e.g., an anode) in a lithium-ion electrochemical cell include lithium-graphite intercalation compounds, lithium-silicon compounds, lithium-tin intercalation compounds, and lithium alloys. While graphite compounds are most common, recently, anode materials with high specific capacity (in comparison with conventional graphite) are of growing interest. For example, silicon has the highest known theoretical charge capacity for lithium, making it one of the most attractive alternatives to graphite as a negative electrode material for rechargeable lithium ion batteries. However, current silicon anode materials suffer from significant drawbacks. Silicon-containing materials experience large volume changes (e.g., volume expansion/contraction) during lithium insertion/extraction. Thus, cracking of the negative electrode (e.g., anode), a decline of electrochemical cyclic performance and large Coulombic charge capacity loss (capacity fade), and extremely limited cycle life are often observed during cycling of conventional silicon-containing electrodes. This diminished performance is believed in large part to be due to the breakdown of physical contact between silicon particles and conductive fillers caused by the large volume changes in the electrode during cycling of lithium ion.
It would be desirable to develop high performance negative electrode materials comprising silicon for use in high power lithium ion batteries, which overcome the current shortcomings that prevent their widespread commercial use, especially in vehicle applications. For long term and effective use, anode materials containing silicon and conductive fillers should be capable of minimal capacity fade and maximized charge capacity for long-term use in lithium ion batteries.